In hybrid launchers, burn speed is of limited relevance, as the "valve" does not open until the desired pressure is reached, regardless of how long that takes. A problem would arise if the burn was so slow that heat transfer to the chamber walls became an issue, but that's not the case with any propellant mixes which have been tried so far.

Detonation could be useful in certain "specialized" cases, but it's never been tested at all (and is agreed to be useless for "normal" launchers). Larda's HyGaC20 suffered a particularly poor shot which appeared to be a detonation, and a few people have had bulged or ruptured barrels which were attributed to DDT. It is important to note that detonation of all or most of the fuel load is essentially unknown to us - local shocks created by the reaction front interacting with chamber geometry are likely responsible for the bulged barrels and all or most of the PVC hybrid "detonations" back in the day.

@RJB: as I mentioned above, "detonation" is something of a sliding scale. All else being equal, hydrogen mixes do detonate more readily than gaseous alkane mixtures, so you will be more likely to see these small bulges and cracks. Unless you're doing something really silly like using a 2:1 hydrogen/oxygen mix, you're unlikely to detonate the entire fuel load accidentally (which would cause damage to any chamber which wasn't very overbuilt).

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Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.

RJB INDUSTRIES wrote:What do you mean with light projectile?Do you think that in a gun the burn rate doesn´t matter jimmy?

RJB INDUSTRIES

Depends on the gun and ammo. For a heavy ammo then burn rate is probably unimportant. For a light ammo, imagine shooting a ping pong ball, then burn rate would be much more important.

Plus, burn rate tends to be linked to the movement of the ammo. Even with a slow burning fuel and a light ammo the movement of the gases as they push the ammo down the barrel will tend to increase the burn rate.

ideally you want slower burn rates for heavy projectiles, and fast burn rates for light projectiles. This is because the heavy ammunition cannot react as quickly as the light projectile and thus, a fast burning propellant would be less effective.

RJB INDUSTRIES wrote:Is too small maybe with butane or propane with H2 I think that you haven´t done calculations yet, I will calculate the energy that is produced by a 0.5L h2 chamber and compare with a butane one.

RJB INDUSTRIES

If you do the calculation correctly you'll find the energy is virtually the same. BTW, you should use "low heat values" and not "high heat values" for the combustions, though the difference isn't all that great. (See for example http://en.wikipedia.org/wiki/Fuel_effic ... nt_of_fuel)